Mr Sinclair, an Ashburton mechanic, and his partner, Christchurch nurse Anna Love, were on the last day of their holiday in Indonesia on Friday afternoon when the ferry they were travelling on from Lombok to the island of Bali exploded.
Allan Sinclair said he understood the explosion blew a hole in the floor beneath where his son and Ms Love were seated. "I have a feeling Paul might have fallen through, down to where the engine was, and apparently it started filling with water and he had to climb his way back up to the top deck to get away from it.
"He's in a lot of pain and it was probably a traumatic experience," Mr Sinclair said.
The couple had been in Indonesia for about 10 days and were travelling to Bali to fly home.
Two explosions rocked the Wahana Gili Ocean 4 ferry about 30 minutes after it left Lombok, according to local officials. Reports have indicated the engine exploded after a fuel line burst.
The stricken vessel was towed back to Lombok by another boat. Eleven of the 129 passengers suffered burns and eight suffered broken bones.
Ms Love, who suffered burns to her leg, helped to treat some of the injured.
"Seats were flying everywhere, people were flying everywhere. We keep having flashbacks about what happened," she said.
Mr Sinclair was carried from the ferry on a surfboard in an attempt to protect his spine from further injury.
The couple were taken to a local hospital before Mr Sinclair was moved to a private hospital, where a scan diagnosed a lower spine compression fracture. They were flown to Darwin on Saturday.
Allan Sinclair said the couple had been fortunate to have reliable insurers.
"They have done a beautiful job getting them flown by air ambulance over to Darwin and organising the private hospital [at Lombok]."
